Owing to the type of missions undertaken, take-off and landing in regions with restricted access, sometimes unprepared, or low-altitude flight, the helicopter, for example, is an aircraft that is highly exposed to the risk of collision with obstacles situated within its near environment. Aside from the geographical aspects, during medical evacuation operations, the use of the helicopter is very often reserved for survival emergency cases for which the speed of action and the continuation of the mission are vital for the victim to be rescued. The urgent nature of the mission and the consequent risk taking lead to increased dangers of coming close to obstacles.
In response, the committee SC-212 of the RTCA (Radio Technical Commission for Aeronautics) aeronautics consortium has defined the minimum operational service provided by a system of the helicopter-TAWS (Terrain Awareness and Warning System) type. The aim of such a system is to generate a warning when the aircraft is in a dangerous situation which no longer complies with the operational margins.
In parallel, the committee SC-213 of the RTCA is working on the definition of the requirements of the EVS (Enhanced Vision System) and of the SVS (Synthetic Vision System). The benefit of these systems is to increase the awareness, by the pilot, of the environment around the aircraft. This is notably achieved via a three-dimensional display of the surrounding relief, which is generated either by the acquisition of data of the infrared type, or from a digital model of the terrain.
The existing solutions envisaged are systems of the TAWS type coupled or otherwise in a conventional manner with a system of the EVS/SVS type.
Systems of the TAWS type are well known to those skilled in the art. The aim of these systems is to generate a warning when the aircraft is in a dangerous situation where it no longer complies with the operational margins. TAWS systems, either as a stand-alone computer or integrated with the TCAS (Traffic Collision Avoidance System) and WXR (Weather Band X Radar) functions, within an ISS (Integrated Surveillance System), fulfil a primary monitoring function for collision avoidance with the ground (“Safety Net”) and have the role of emitting audible alarms during an exceptional proximity of the ground terrain allowing the crew to react by engaging a vertical resource before it's too late. For this purpose, TAWS systems, decoupled from navigation systems, operate in two ways. They periodically calculate the theoretical trajectory that the aircraft would describe during a resource and compares it with a cross-section of the terrain and with the obstacles overflown obtained from a digital model of worldwide or local terrain loaded on board the computer. Alternatively, some TAWS systems also incorporate modes known as “reactive modes” in which, by periodically comparing certain of the current parameters of the aircraft, for example the radio-altitude and the vertical speed, various charts determine whether the current situation of the aircraft is a normal situation or whether it is potentially dangerous. In the latter case, a warning, limited to an oral message, is generated in order to inform the crew. The availability of a model of the terrain enables functions that allow the crew's awareness of the situation to be improved. Amongst these, Alert Lines are used to delimit areas of terrain for which a TAWS alert is liable to be raised. As regards the “Alert Areas”, these show the areas causing a TAWS alert.
Numerous Patent documents describe this type of system. Amongst these may be mentioned the Patent EP0 565399B1 describing all of the basic concepts of TAWS systems and the Patent application US2003/0107499A1 describing a device for displaying hazardous areas of terrain capable of causing a TAWS alert.
When a TAWS system is not coupled to a system of the EVS/SVS type, the display of a TAWS is often presented in two dimensions in the form of areas of colour. Some thought is therefore required by the crew in order to make the link between the information displayed in 3D by a system of the SVS/EVS type and that displayed in 2D by a system of the TAWS type.
When it is coupled to a system of the EVS/SVS type, the existing couplings are very often based on placing the regions of colour calculated in two dimensions onto the three-dimensional structure used to represent the terrain and the obstacles. Owing to the difficulties associated with the interpretation of the 3D symbols, these couplings based on coloration requires some thought by the crew in order to determine with precision which area is to be avoided and which manoeuvre allows them to achieve this.
In addition, the display resolution of the three-dimensional space often differs from that of the two-dimensional space. This results in display for the hazardous areas in three-dimensional space when these hazardous areas have been initially calculated in a two-dimensional space of lower resolution. For example, the U.S. Patent Application Publication No. 2004/0160341 is known which proposes a solution for coupling a system of the TAWS type and display system of the SVS type.